Abstract

Most of the original applications of reverse-time migration were on CMP (common midpoint) stacked data. The method found use in oil exploration near steeply dipping salt intrusions (Whitmore and Lines, 1986; Lines et al., 1995; Mufti et al., 1996) and overthrust fold belts (Whitmore, 1983; Bording et al., 1987; Lines, 1993; and Wu et al., 1996). To the extent that the CMP stacked data represent the zero-offset sections of an exploding reflector, model studies (eg. Bording et al., 1987) show that reverse-time migration can do an excellent job.

CMP stacking encounters its worst problems in representing CRP (common reflection point) data whenever geological structures deviate most from at layer geometries. With the fact that CMP does not equal CRP for such geometries, one might wonder why stacking would work at all. However, fortunately for geophysicists, CMP stacking is reasonably robust for mildly complex structures, as shown by Kelly et al. (1982).

Another method of alleviating the problems of steep dip in processing is the use of DMO (dip-moveout). Ideally the use of NMO (normal moveout) corrections used with DMO corrections and CMP stacking allows poststack migration to perform as well as prestack migration at considerably less expense. The benefits and advantages of using DMO are summarized by Hale (1991).

The most general (and most expensive) imaging technique which is available in the migration tool box is the process of prestack depth migration. The use of this powerful method necessitates the use of accurate velocity models. In fact, as we will see in the next chapter, prestack reverse-time depth migration will be used as a velocity analysis tool.

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“Seismic modeling and imaging of the earth's subsurface are complex and difficult computational tasks. The authors present general numerical methods based on the complete wave equation for solving these important seismic exploration problems.”